DIFFERENTIATION BY MAGNESIUM-IONS OF AFFINITIES OF NUCLEAR PROTEINS FOR CONSENSUS CORE NUCLEOTIDE ELEMENT OF THE TRANSCRIPTION FACTOR C-MYCIN MURINE BRAIN

The addition of divalent cations such as Mg2+ and Ca2+ ions markedly r educed binding of a radiolabeled double stranded oligonucleotide probe for the transcription factor c-Myc in the presence of 100 mM KCl in n uclear extracts of the mouse whole brain, Irrespective of the addition of MgCl2, binding was selectively competed with the unlabeled probe f or c-Myc having a double stranded conformation. Treatment with Vs prot ease differentially modulated binding of the probe for c-Myc determine d in the presence and absence of added MgCl2. Introduction of irrevers ible covalent bonding between the radiolabeled probe and nuclear prote ins led to retarded mobility of the radioactive probe/protein complex in the presence of MgCl2 on sodium dodecyl sulfate electrophoresis reg ardless of treatment with DNase, However, an antibody against the c-My c protein affected neither mobility nor intensity of the radioactive b and on gel retardation electrophoresis. Moreover, regional distributio n was different from each other in mouse brain when determined in the presence and absence of added MgCl2. These results suggest that magnes ium ions may have an ability to differentiate between nuclear c-Myc fa mily proteins with different affinities for the consensus core nucleot ide element CACGTG in murine brain.